1. Field of the Invention
The present invention relates to measurement of light.
2. Description of the Prior Art
There has conventionally been known a method for measuring a device under test by a terahertz detector receiving terahertz light A (in a form of pulse) which has been fed from a terahertz emitter to the device under test, and has transmitted through the device under test, and light B having the pulse period which is slightly different from the pulse period of terahertz light A (refer to ABSTRACT of Patent Document 1, for example).
When the repetition frequency of the terahertz light A is fA and the repetition frequency of the light B is fB, a time required for measuring one period of the light pulse which has transmitted through the device under test is represented as:1/(fA−fB)[s]
Moreover, a measurement of a signal using a spectrum analyzer is widely known. The spectrum analyzer measures the power of a signal for respective frequencies. The frequency at which the spectrum analyzer carries out the measurement changes over time. In other words, the spectrum analyzer sweeps the frequency for the measurement.
(Patent Document 1) WO 2006/092874, Pamphlet
Then, it is conceivable to measure the signal detected by the terahertz detector by the spectrum analyzer. The frequency for which the spectrum analyzer carries out the measurement is represented asfs+n·S/(fA−fB)[Hz]where fs [Hz] is a frequency from which the spectrum analyzer starts the sweep, and S [Hz/s] is a velocity of the change in the frequency for which the spectrum analyzer carries out the measurement (it should be noted that n is zero or a positive integer).